1. Field of the Invention
The present invention relates to a process cartridge and an image forming system or an image forming apparatus within which such process cartridge can be mounted. The image forming system may be an electrophotographic copying machine, a laser beam printer (LBP), a facsimile system, a word processor or the like.
2. Related Background Art
In the past, an image forming system having a removable process cartridge including a desired process means necessary for forming an image, thereby permitting the easy replacement of the cartridge due to the expiration of the service life of the cartridge or the like has been proposed (refer to U.S. Pat. No. 3,985,436). Further, a plurality of process cartridges having developers of different colors therein can be used to form a color image, and, thus, have a high frequency of exchange, and, in some cases, the process cartridge alone is disposed outside the image forming system. Under these circumstances, it is necessary to prevent the photosensitive member from being smudged or damaged and to prevent the photo member from being exposed to light (which leads to the deterioration of the photosensitive member). To this end, the process cartridge is provided with a cover member for protecting the photosensitive member and shielding the interior of the cartridge from ambient light.
Inventors invented the particularly effective techniques in this technical field and disclosed them in U.S. Pat. Nos. 4,470,689 and 4,462,677. The present invention relates to the improvement in the above invented techniques.
Now, the background art for the present invention, that is, art of the process cartridge, will be described with reference to FIGS. 1 to 3.
FIG. 1 shows a process cartridge 3. A photosensitive drum 4 disposed in the process cartridge 3 is easily overcome by shock and frictional wear. Thus, normally, a drum shutter 20 is provided at a transfer opening 3a of the cartridge 3 and the photosensitive drum 4 is protected by the drum shutter 20. Incidentally, when the cartridge is inserted into an image forming system, the drum shutter 20 is shifted from a closed position to an open position,(shown by the broken line 20a), thus permitting the transfer of an image formed on the photosensitive drum.
The closed position of the drum shutter is limited or regulated by abutting a projection 20b of the drum shutter against an end 7a of a cleaner 7. The reference numeral 21 denotes a shutter arm.
However, the width of the drum shutter 20 is long (for example, in a process cartridge 3 capable of forming an image on a sheet of A4 size, the width L is about 270 mm, and, in a process cartridge 3 capable of forming an image on a sheet of A3 size, the width L is about 350 mm). Further, the drum shutter 20 is generally formed from the engineering plastics. Thus, when the cartridge 3 is dismounted from the image forming system 2, if an operator grasps the process cartridge 3 by his hand as shown in FIG. 2A, a central portion of the shutter 20 will be flexed as shown in FIG. 2B. Accordingly, it was feared that the drum shutter 20 would contact with the photosensitive drum 4 (FIG. 2B), thus damaging the latter. To avoid this, as shown in FIG. 3, a protection sheet as a drum guard 23 for protecting the drum is adhered to an inner surface of the drum shutter 20 to protect the drum. However, even in this case, it is difficult to completely prevent damage of the photosensitive drum 4 due to contact between the drum and the drum shutter 20.